Four-point control arms of the type mentioned in the introduction have been used for some years especially in trucks and other utility vehicles. Such four-point control arms combine in only one component a number of functions and tasks, for which a plurality of control arms or components were necessary before in the area of the axle guide.
The need for additional roll stabilizers for roll stabilization of the vehicle body is eliminated, among other things, by the use of a four-point control arm, because the four-point control arm assumes, for example, together with the existing longitudinal control arms, both the task of axle guiding in the transverse and longitudinal directions and the task of absorbing torques and roll stabilization. The previously necessary three-point control arm can be eliminated as well. Thus, both the design effort and the weight of the vehicle are reduced to a considerable extent, which leads to reduced costs for manufacture, operation and maintenance of the utility vehicle.
Since roll stabilization by the four-point control arm does not take place, unlike in the case of the torsion bar, mostly behind the vehicle axle, but it can rather take place by means of the introduction of force into the vehicle chassis mostly in the area located in front of the vehicle axle, the vehicle may not, moreover, optionally require a reinforced closing cross arm either for absorbing rolling torques. This leads to additional cost savings and weight reductions.
Based on the sum of these advantageous properties, the four-point control arm, which usually has a cross or X shape for reasons of manufacturing technology, for cost and strength reasons as well as for reasons of low component weight, has become successful and widespread in an extremely short time, especially in the area of heavy utility vehicles.
Both forged four-point control arms and four-point control arms made of sheet metal as well as casting have been known in the state of the art, for example, from DE 195 21 874 or DE 102 06 809. However, there usually is a substantially more massive rectangular cross section for the arms of the four-point control arm in case of the forging process, which leads to heavy weight of the component and to high manufacturing costs associated therewith as well as to increased fuel consumption and reduced payload of the utility vehicle.
Built-up or welded four-point control arms are likewise complicated and consequently expensive to manufacture. By contrast, prior-art four-point control arms, which are designed as castings, see, for example, FIGS. 7, 8 or 11 in the document DE 195 21 874, are likewise complicated from various points of view and can be manufactured less reliably. Thus, in four-point control arms with closed cavity geometry, there are only very limited possibilities of supporting the cavity-forming cores in such a way that the cores will not float during casting and therefore will not cause nonuniform wall thicknesses in the casting, which would correspondingly lead to unfavorable strength properties. Due to the same problem, such cast four-point control arms cannot be manufactured with the large cross section and therefore small wall thicknesses which are desired in terms of lightweight construction, which in turn leads to castings or four-point control arms with a needlessly heavy weight.
Other four-point control arms, for example, the four-point control arm which is shown in FIG. 11 of the document DE 195 21 874 and can be manufactured especially by casting, requires a plurality of cores for the manufacture, which in turn makes the manufacture complicated and therefore expensive. Moreover, due to the cavities present, the four-point control arm shown here cannot be optimally adapted to the prevailing load situation, which is characterized mostly by a combination of shear and bending, but is especially associated with high torsional loads.